Brake master cylinder rebuild–II. Reassembly.

2017apr00-1With the master cylinder bore honed smooth, everything can be put together.  Thankfully, the brakes don’t need a jerry-rig to get back into shape; remarkably, Napa still makes and sells off-the-shelf rebuild kits for brake systems this old.  It was merely a matter of walking up to the counter and placing the order.  Had it in my hands the next morning; gotta love America and mass production—auto parts off the shelf.

Here is the content of the rebuild kit, laid out against the same parts from the disassembled cylinder assembly. To all appearances, the parts are identical.  I was more than a little surprised to note that the primary seal looks like it was even cast on the same mold, so maybe the brakes have been rebuilt at some point in the past more recent than “never.”

All but one of the parts—the spring, into which the valve assembly snaps—have a replacement part.  As mentioned, I want to use original equipment, reconditioning it if necessary, so the secondary seal came off the new piston and was put onto the original that I removed.  The old valve assembly snaps out of the spring and the new one snapped right into place.  One that was in place the innards were assembled as shown in the images.

Keep in mind that the piston and seals don’t just drop in place; they have to be pushed because they fit tightly into the bore.

Once the piston, seals, spring, and valve are in place the challenge becomes assembling the mechanical linkage. The pushrod assembly has a plate at one end that seals off the mechanical end of the master cylinder. The pushrod itself has an acorn head that engages the cupped end of the piston with the secondary seal.  Because the two pieces are not threaded or locked, the pushrod can turn and moves at a slight angle when the brake is engaged. That freedom of movement allows the pushrod to be turned with the knurled nut on the shaft allow it to be threaded into the fork on the brake shaft (today we’d probably just make the shaft hexagonal for a wrench). The boot threads over the knurled nut on the pushrod.  The round plate on the assembly fits into the end of the brake cylinder.  The snap ring holds it in place, and then the boot covers everything.  Won’t say how many times I took it apart because I missed something.

So here are before and after shots of the brake master cylinder, both taken as if looking at it from the driver’s side.  The plunger at the left is the link to the brake pedal (the fork visible in the “before” picture got removed and put back onto Green so I didn’t lose it).  The brake line itself threads into the cap on the right end.

Here is a section of the complete assembly from the shop manual, shown in working order for context.


And that’s that.  Ready to go back onto the Green Truck.

Brake master cylinder rebuild–I. Honing.

Thanks to my patient reader (notice the use of the singular noun there) for not removing The Green Truck from your blog roll, despite the lag in substance this spring.  If there are more than one of you out there, well, great.  Hopefully action on the blog will pick up again.  This is a good place to start.

I talked about removing and disassembling the brake master cylinder in an earlier post.  This one continues the process in two parts:  the first one on reconditioning the bore, and a second one on reassembling the master cylinder (and hoping it is in working order).

Green rarely had servicing and what was services used to be fixed with baling wire (and yes, there are still pieces to be seen holding this or that together).  I’ve mentioned that there are absolutely no brakes–not a drop of brake fluid to be found in the lines.   Brakes are high on the list of necessaries on an automobile, so obviously something needed to be done.  I’ve been trying to find time to do this for six weeks, but I came home an hour early on a Friday afternoon and press-ganged Son Four into acting as a photographer so that I could document the work.

The bore of a brake master cylinder is normally smooth.  As you can see (below), the cylinder walls from Green’s cylinder are hardly smooth any more.  What has happened is that over time a tiny bit of moisture in the line has pitted the steel sides. That rust creates depressions that allows brake fluid to leak past the primary seal.  Pushing on the brake pedal becomes less effective because the hydraulics are compromised and don’t transfer the force effectively to the brake cylinders in the wheels.


Pitting in the bore.

The brakes were failing as I drove Green in high school in the late 1970s and early 1980s. Thirty-five years of sitting in a field hasn’t helped.  To again function correctly the cylinder bore has to be smoothed out or replaced entirely.  Since I am trying to keep the original equipment on Green, the available options were fairly direct–the cylinder has to be honed smooth. Honing a cylinder is technologically simple but requires a specialized tool that would be used once and never again.  I still bought one.

A hone is nothing more than a trio of small grinding stones set on springs at the end of a shaft. Having three spring-loaded stones keeps them centered evenly against the bore walls as the shaft turns.

The challenge of honing a bore is to stay within tolerances:  just enough steel has to be removed to level the pits, but not so much that the primary and secondary seals no longer fit tightly.  After doing some exploring, the folks who have done this say that one aims at taking off no more than 0.004 of an inch, which enlarges the bore by twice that figure or 0.008 inches, because there is a bore wall on the opposite side as well.

Notice that the hone fits into a standard drill.  I could have maybe used a hand-operated eggbeater drill, but that would have been difficult to both hold and operate effectively.  As it was, I had to use both hands and compromised on the setup–I was supposed to use solvent to flush away the particulates from the grinding and prevent oxidation, but I followed DIY advice to use hot water, since I don’t have a shop solvent fountain.  Son Four did a thirty-second video of the hone in action, but my WordPress subscription does not allow me to post video files, so here are a couple of stills that show how it works.


After the bore was honed and while it was still wet, the cylinder went into the oven to dry it out quickly.  As it was there was still a film of oxidation (rust), which I wiped out first with a shop towel and then a bit of brake fluid to coat the steel and keep it from oxidizing again.


As you can see in comparing the two images, there are still a few shallow pits, but conventional wisdom is that something that small probably won’t affect the breaks much because the primary seal should be flexible enough to ride through them.

So, now all that needs to happen is to put everything back together.


Ok–so we’re back from the China trip, Scout camp, and as of yesterday I am back from the week-long RBMS conference at Iowa City.  I am ready for a rest and to get back to The Green Truck.

Or not.

After a lot of thought I’ve decided that the motor really needs to be overhauled before I tackle most of the body work.  To do that properly will require an engine hoist and stand, plus some disposable income and time.  I’ll have to pull off the hood, fenders, and cooling system to get at the motor mounts in the workspace I have.  I’ll need to build the special hoist frame required for the stovebolt motor.  I’ll have to replace the wiring completely so the motor will run properly from the cab, which means new fuses and probably gauges.

So, this may take awhile–but hey, its a DIY learning experience, and there are no time limits on that.


China, from my perspective.

Well, we’re back from China.  Before I go back to Green, let me give at least a quick impression of my experiences in the most populous country on earth.

My long-held impression of modern China came from an old twelve-part PBS documentary of the 1980s called Heart of the Dragon, one of the first extended views into post-Mao China afforded westerners. It certainly captured my attention and shaped the experience I expected. Won’t say I was disappointed, but I will say I found something very out of my ordinary.

What I found was a country thoroughly commercialized, albeit in a different form than the American version of drive-up windows, franchises, and corporate empires.  There are millions of street-level small businesses tucked into every building, some only a few feet deep or wide.  The cities are full of Western brands and particularly luxury goods.  Since this is an automotive blog I could not miss photographing the one mechanic’s place I saw.  Even fueling stations were rather uncommon.

Truthfully, I expected to see reproductions of the old American vehicles copied for decades by Chinese factories.  They had done that for decades, but nope–not a one.  Mercedes, Buick, Hyundai, Russian, and Chinese knock-offs were everywhere.  Every street and intersection was filled bumper to bumper.  Traffic was a much more intimate experience than I am used to. The streets are filled with sedans.  SUVs are popular, but I saw not a single pickup truck during our 10 days in the country.  I expected to see streets full of cyclists.  There were lots, but many were riding rentals.  I saw not a single Mao Jacket, though I looked constantly.

China 2

The first billboard we saw leaving the airport–was for the Green Truck’s distant cousin from the Chevrolet family.

Shanghai (our first stop) is a city of 25 million people, better than twice the population, area, and density of the Chicago metro area, and China is modernizing quickly–very quickly.  Shanghai is filled with 30-story apartment blocks everywhere and many, many more going up.  In a single development by the Hangzhou airport (second stop) I counted no fewer than 36 gantry cranes, and it was one of dozens being built.  This is why concrete and diesel prices are skyrocketing in the US–the real market is China.  In most cities there are still pockets of old neighborhoods, warrens of narrow alleys and walkways (two were visible from our hotel room) capped with terra cotta tiles of that distinct, ribbed Oriental look, but they are being replaced as quickly as construction can manage. From what I hear, the old buildings are not mourned:  they have neither kitchen nor restroom facilities–they are the Chinese equivalent of tenements.

Of course I have to say something about food, which was terrific. We did not get an opportunity to eat as often on the street as I would have liked (and we were strongly advised against doing so, anyway).  I did try chunks of jackfruit, hawked off the back of a motorbike, and we had noodles for lunch one day in the walk-up place outside our hotel in Xi’an (third stop).  As a rule, we didn’t get much of a chance. We were feted afternoon and evening.  It was a wonder I did not gain 30 pounds.

This image was taken at about the middle of the meal. By the time we were done I counted nineteen different dishes on the table.  I am grateful I took time to learn to eat effectively with chopsticks as a teen.  They expected it from Dear–she had lived in Taiwan; how well I was did was noticed more than once–even with noodles.

A few more pix than the ones shown here appear on my Facebook page, and the return flight is a tale in itself.  I have hundreds more photos and could have taken millions without really documenting China.  Dear and I had a very good time, but China is changing so rapidly that if we ever have a chance to go back, China will already be different.



A sense of scale.

Lest I miss another week, let me add a sidebar comment that puts this automotive project into perspective.  There probably will not be another post here till mid June, since in a week my wife and I head to China on a business trip.  That’s another story entirely, one that has nothing to do with perspective or the Green Truck.

Last week I was unable to write because I was in Ogden seeing a train and to receive a donation from the Union Pacific Foundation on behalf of Southern Utah University. They fed us lunch on the train and we had plenty of time to walk around and see it from most sides. Even got a look into the cab.  I’ve been in these before, there was an engine to climb on in a city park of my childhood home, but typically everything was painted black and nothing moved.  This one moves.

This is UP 844, the Union Pacific Rail Road’s last steam engine, delivered in 1944 to the company that built the overland railroad in 1869. The cars are restored to their mid-century glory as long-distance transportation.  There is leg room to the point that one has foot rests to be comfortable.  This ain’t no 737.  Yes they blew the whistle–the deep, throaty wail that everyone should hear occasionally. The nasal air horns on a diesel locomotive are purely utilitarian, they just don’t have emotion in them. One does not understand “the lonesome sound” memorialized in American roots music until you hear a steam whistle blow a long, tapering wail.

Plus, you have to admire a vehicle that carries around its own maintenance shop. The sense of scale of these iron monsters is just not really comprehensible until one gets up close.  Now remember, I am six feet tall.  That drive wheel behind me, cast steel better than five inches thick, weighs more than half a ton by itself.  The interior of the fire box, the studded section above my left shoulder, is larger than the desk space in my office.  Compare this photo with the blog’s lead photo to help with a sense of scale.

Train 4

This is a seriously large machine, mechanical poetry conceived in the passion of engineering, born in the fire of mid-century American industry, and draped with romance.  This–this is a train.

Brake hiatus.

It has been a couple of weeks since my last post. Mostly that is because I have not had time to do anything substantive at all.  Too busy at the library, and desperately trying to complete abstracting microfilmed correspondence for the biography on which I have been working (or telling people I am working) for a quarter-century now.

I did some other 2017apr23things.  Took back the Evercraft SAE combination wrenches (Society of American Engineers or imperial standard; i.e., inches and fractions) and instead bought a set of Craftsman with both SAE and metric wrenches, having got a terrific deal on them.  That means with the snippets of time at hand I’ve begun to reset the top drawer of the tool chest.  Pictures later, right now I have to find time to get the drawer lining reconfigured so the wrenches go neatly into place.  Yes, OCD (just a bit).

This week I also bought a bore hone for the brake master cylinder and wheel cylinders (if they need it).  Tried to borrow one but couldn’t.  Have not taken it out of the package, however, because I cannot use it without someone else to take photographs.  Not only don’t I have time but I don’t have three hands.

Probably won’t get the brake cylinder honed this week because I am on the road for state consortium meetings and development work.  No rest for the wicked–or for a dean, for that matter.  Maybe that’s the same thing?

2017apr23-2[Update]  I finally finished setting the drawer for the set of Craftsman open-ended wrenches I bought to replace the set I returned.  I really like these, not least because when I run a fingernail up or down the row I get an ascending or descending musical tones.

The yellow mats are two of the kids’ old play tiles, about half an inch thick and much nicer than the black stuff for those with failing eyesight.


Master cylinder disassembly

You’ll recall that the end plug to the brake master cylinder would not come out.  In the interim the workbench was built and the tool chest installed.  Even with the shop vise in place it still would not move.  Nor is the work optional. Remember I said that Green essentially had no brakes when I last drove him in 1980s.   The end plug has to come out so that the brake lines can be rebuilt.

Seven decades of ignoring maintenance has clearly taken their toll.  So how does one “thaw” frozen steel parts?  A propane torch and a gentle touch (mostly the former).  Steel expands when it is heated, so a couple of minutes invoking the blue flame and with the good offices of a pipe wrench, and it broke loose.

With the end plug removed it was a simple matter to remove the spring and various caps and seals.

So here is what it looks like in an exploded view on the work bench.



Well, it’s a beginning.  I have not yet ordered the rebuild kit, which will supply new gaskets and seals. Most of the metal parts will go back into place.

One of the key parts is visible at the bottom.  The piston holds the primary seal, a cap, at one end and the secondary seal, a ring, around the other.  It is cast aluminum.  I took a small wire brush to it to ensure corroded grit would not get back into the brake lines.  I think it cleaned up rather well.  In doing so I noticed a number cast into one side of the piston shaft:  24887.  I assume it is a part number, though the service manual does not say.

My chief concern is the master-cylinder bore.  Having had no preventative care and having sat unmoving since at least 1987, the real problem is the inevitable corrosion along the walls where the rubber seals trapped moisture in the system. You can see a spot of that bright red-orange gunk on the cylinder wall just as the piston was removed.  The other image shows the bore after I scraped the walls with a flat screwdriver to see what would come loose, and brushed it with a small steel brush.

Those small pits are a problem.  The bore can be honed a bit to take off surface scoring, but the pits will not allow the seals to fully seat against the walls, allowing a small bit of leakage that over time will weaken the brakes.  I plan to borrow a hone, but can take off less than the thickness of a sheet of tissue paper.  To much, and the piston seals won’t handle the pressure and brake fluid will leak past them.  The cylinder will be ruined and I buy a new one.  Since my goal is to bring Green back into running order with as much original equipment as I can manage, I will be really careful.


Another shop feature.

As I wrestled with the master cylinder end plug it was clear that I needed a stable workbench.  The best vise in the world isn’t much good if it hops across the floor when something in the jaws is torqued.

So, I took time out and built a sturdy bench last weekend. The top is scrap 2x4s from the local big-box with the edges sawed flat for gluing. It is edged with 2x4s and the legs are glued and screwed in place.  The whole thing knocks down, as well—the top lifts off, the cross brace in back is unbolted, and the whole thing can be stacked away easily, if necessary.  The vise was installed at one end, but I drilled holes on the opposite side for a duplicate mounting position as well so it can be moved to the other end.

Part of the reason for the bench was that I’ve also been eying a suitable rolling shop tool chest.  I still have dad’s old Craftsman steel toolbox and won’t part with it, but as Jane Austen points out presciently, “It is a truth universally acknowledged, that a hobby mechanic in possession of a good truck project, must be in want of a tool chest.”  Or something like that.  So the bench provided a reason (or excuse) for another toy.

I’ve been periodically looking at a small chest at Home Depot for several weeks. One of the reasons the workbench is built like it is, is that I could set a small chest under the work surface if the wheels were not mounted.  The one I’ve looked at was $179 and had five drawers of varying sizes.  The odd thing was that I could not bring myself to buy it.  Now I know why.  Dear came home one day this week to say the store has been running a sale and one of the advertised items is a larger chest of nine drawers.  She suggested now would be a good time to buy one.  My word—what kind of husband would I be to contradict my wife/accountant in such a circumstance!  We bought it this morning.


Son Four helped (reluctantly) get it unpacked.  Didn’t want it to sit directly on the concrete so I cut a pair of feet out of a piece of 2×2 Trex to serve in place of the casters to keep the steel off the floor, which brought the surface up to the 32″ clearance beneath the edge of the table top—exactly.


So, now I just need some tools. . . .

[Breaking news (8 Apr 2017]

Added one neat feature that I’d encourage for any tool chest, a foam drawer liner with cutouts to hold everything in its proper order.  No rummaging through the drawers for something you can’t see.  Neat as a surgical setup.

The chest came with drawer liners of 1/16-inch foam. With it in place tools won’t rattle and scratch the drawers, but I put in an added insert re-purposed from a couple of old floor pads.  They used to sit in front of the stove to lessen the stress of standing there, but an accident spilled oil all over them (vegetable, not motor) so they really don’t belong on the floor any more.

I simply cut them to fit the 41-1/2 x 15-3/8 dimension of the drawer, positioned tools where I wanted them, traced around them with a pen, and used a utility knife to cut out the shapes I wanted.

Some basic tools now reside in the top drawer:  the socket set—bought for my first automotive adventure in 1994 (another tale entirely) and several well-used Channel Lock pliers were moved from their long-time previous home in my dad’s old toolbox.  The Napa Evercraft screwdrivers and combination-wrench set are new—lower-end goods, to be sure, but adequate for the rank-amateur weekender that I am,  and intended for automotive work, at least.


I like it. One does not have to go looking to know where a tool is, and it provides visually clear reference to see if something is missing.  Yes, it gratifies my native OCD-ness.

Brake master-cylinder dismount.

Well, it’s spring break.  I spent some quiet time at the office doing administrative necessaries, some time at home reading microfilm, and on the last day of the break I took a break and just said “time to work on the truck.”  So I did.


The job I chose was to remove the master brake cylinder, which is the mechanism that turns kinetic energy (leverage from pushing on the brake pedal) to the hydraulic pressure that powers the drum brakes in all four wheels.


Here is a period film demonstration on automotive hydraulics; toward the end it uses an identical Chevy brake cylinder as a power source.

Reminiscent interlude:  Once I decided to do something marginally interesting for a date.  This would have been in the summer of 1980, before I kept a diary, so I can’t check for specifics.  I got Blair Mumford to get a girl as well.  I drove Green home from Hilltop (Grandpa didn’t drive much, and never in Green those days, so getting it was merely a matter of telling Grandma I was taking it), put a porch love seat in the bed for extra seating, picked up a young woman who could well have become Mrs. Saunders, and took a double date up the canyon to cook a dutch oven dinner.  The brakes, which were always little light, were almost not there.  I had to really push hard, and well before a stop sign or corner, to slow down.  When Grandpa found out I’d taken three other people up AND DOWN the canyon he almost hatched kittens.  I had not known the truck was unregistered because it essentially had no brakes and could not pass a safety inspection. Yes, “I could have killed somebody.”  It must have made a difference because she tossed me over without a backward glance for someone else two years later.

Fast forward thirty-five years. Like I said earlier—Green has no brakes at all.  Looking at the present condition of the master cylinder, even before it came off, it is pretty clear why.  The seal cap on the front, through which the plunger runs, is split clear off (you’ll see it below). It would take merely a good tug to remove it. The cylinder has to be removed, cleaned, and rebuilt entirely.  Yes, I could buy a new one for about $130, but what is the fun in that?  Rebuild kits are about thirty bucks and this is a learning experience, isn’t it?

So, I started back in January by giving the mounting bolts a good soaking with WD-40 and let them sit. This afternoon I simply loosened the bolts, disconnected the brake line and off it came—bone dry.  Not a drop of brake fluid in the line anywhere.  That’s why there are no brakes. You can also see that one of the split washers really was split.

So here is the master cylinder, the mounting bolts and everything else that came off (front is the linkage fork). Obviously the cap–which should seal off the plunger at the front of the unit—will be replaced in being rebuilt.



It needed a good brushing to start with, which took off most of the dirt. It will still need to be actually cleaned. Started on the job by removing the triangular snap ring that kept the external plunger in place at the linkage end. The plunger engages the piston inside (which I neglected to photograph) and simply floats free between the brake linkage and piston, one end restrained in place by the spring clip and retaining washer-thing.


I don’t yet have the rebuild kit on hand, but since I started the blog talking about numbering, I might as well continue the tradition.  The end of the cylinder has “MODEL | 361-J” stamped around the end, as you can see.  The cap has the usual and expected industrial/corporate imperative to “USE G.M.C. BRAKE FLUID”.  Obviously nothing else will do.

The driver or left side has both the Delco name (GM’s parts manufacturer) and “MADE IN USA” cast into the side.  On the opposite side of the body is the part or component number:  5450830 R2 (maybe B2, I can’t tell clearly).  Below it is cast one important detail:  1 1/4″ DIA—or that the internal bore is one and a quarter inches.  That little detail is significant, because the tolerances inside are measured in thousandths of an inch, and there is a good chance, since the cap is in such lousy shape, that the sides of the cylinder will be rusted badly enough that they can’t be honed out without making the bore too large for the piston and caps; brake fluid should not pass around the caps or the braking action will be compromised. Below that, on what looks like a plate screwed onto the mold, is probably a casting-date code. There are two characters which can barely be made out, even in good light, which look like “1-6” or “7-6”. No clue how to read it.

I put the cylinder into a shop vice to remove the end cap but encountered two problems. First, that I don’t have a wrench large enough for the 1-9/16″ nut dimension (other than slip-joint pliers); second, that it is snugged down really, really well.  I cannot get enough leverage with pliers to budge it.  There also seems to be a babbit or lead washer or something between it and the housing.


Try as I might, I could not get into the cylinder itself, so I’ll save the rebuild for another post.

Transmission sludge.

Back from a week’s research in Salt Lake City and another week in California on library business, I decided to start mechanical work by changing the transmission fluid and the oil.  To do that, I bought an oil-change pan from O’Reilly Auto Parts.  Less than ten bucks, and it allows me to collect and haul oil to a recycle center so that it doesn’t end up in a water table somewhere.


There are different designs, but I bought a small one. You’ll notice that the top screws off and a screen keeps drain plugs from dropping into the body as it drains. Transmission fluid is a lightweight hydrocarbon, meaning it is a very thin, light and almost clear oil that does not evaporate like gasoline.

Started by draining the transmission; ultimately I will have to similarly drain the oil, radiator, and fuel tank, but I expect after 36 years of sitting outdoors in the sun the fuel has evaporated.

Green is up on jack stands so I have room to work underneath him.  The plug came out with a bit of effort and I was surprised that the liquid that spurted out—was water.  About a third of a cup, I’d guess.  Water is less dense than oil, so it pooled at the bottom of the transmission case, first out of the drain. How it got there and how long it has been there, I have no clue.  It wasn’t rusty, but it came out so quickly I could not get a picture.

What I did manage to photograph was the slow, steady stream of blackish-brown gunk that drizzled out. Now I know that Green has sat in the farmyard for better than three decades, so the transmission fluid could not have been changed since at least 1987.  It was so dark and viscous that I am tempted to believe it is the lubricant I was driving on in the 1970s.  It would not surprise me if it has been there since before R. Welling bought the truck in 1973. Stuck a screwdriver into the drain hole a couple of time to encourage soft clumps of congealed oil.  Anyway, after watching it slobber into the pan for half an hour without finishing, I left it draining overnight.

Clearly it will need to be flushed to get it cleared out properly, but when I took in the oil for recycling today the mechanic said no, just run it for awhile with new fluid in it and then change it.  I was too nice to tell him it will likely be years before Green needs transmission fluid to go anywhere.